A conventional mouth piece assembly for container known to applicant discloses a mouth piece assembly that is pivotable relative to the container such that the user can suck the liquid in the container at different angular positions. The disclosure includes an elbow-shaped member which is connected between a valve and a pipe into the container. The valve is connected with the mouth piece and has a stop flange which is cooperated with a seal member which seals the outlet of the container. The valve includes an inlet which in communication with the mouth piece when the elbow shaped member is rotated to a position, such that the user can suck the liquid in the container. The mouth piece is isolated from the valve when the elbow-shaped member is rotated to another position. However, the maximum volume for the user to suck the liquid in the container is only happened when the mouth piece is rotated to the 90-degree position and the volume is reduced along with the angle that the mouth piece is rotated. In other words, the mouth piece assembly simply is a switch to seal the communication of the pipe into the container by rotating the mouth piece.
The present invention intends to provide a mouth piece assembly which provides sufficient and constant volume of liquid that can be sucked from the container via the mouth piece assembly regardless of position of the mouth piece.